1. Field of the Invention
The present invention relates to a radio telephone apparatus which performs radio communications, more particularly to a power-saving control of a transmitted output in the radio telephone apparatus.
2. Description of the Related Art
A power-saving control of a transmitted output typified by a PHS radio telephone apparatus has been heretofore performed by limiting a dynamic range of a detection circuit provided therein. However, the method to limit the dynamic range of the detection circuit has been able to lower the transmitted power by 15 to 20 dB at most.
Accordingly, when a power-saving control exceeding 20 dB is required, a method has been employed, in which a fixed bias voltage is applied to a voltage control variable attenuator constituted by a pin diode and the like provided in a RF stage of a transmission system, and the power source of a driver amplifier is cut off, whereby a gain of the transmission system is lowered and the transmitted output is set to a predetermined power-saving output.
However, in the foregoing power-saving control method in the conventional radio telephone apparatus, during the power-saving control, an auto power control circuit (hereinafter, referred to as an APC circuit) in which a feed back loop is formed is in an OFF state, so that there is a problem that a variation in a gain of an amplifier in the transmission system owing to an ambient temperature change directly becomes a variation in the transmitted output, and a stable transmitted output can not be acquired.
Moreover, when a temperature compensation for the foregoing transmitted output is conducted, there is a problem that a circuit structure becomes complicated.